I saw that one of the forum members took the BMW Performance carbon spoiler for the X6 and it fits pretty nicely apparently.
Or go for the OEM M6 spoiler and have it wrapped in real carbon... not cheap but looks amazing!

I feel the new M6 deck spoiler is discrete and will look great on our Coupe next Feb. Also ordered the CF mirror covers. The CF wrap would look great on the lighter colored cars but kinda gets lost on the dark colors. IMO